Our ongoing research on the biology and function of the RNase A family of ribonucleases is focused on understanding their mechanisms of action in health and disease. The eosinophil secretory ribonucleases, EDN and ECP, and their mouse orthologs, the eosinophil-associated RNases, feature prominently in our discussion of eosinophils and their roles as immunomodulatory mediators in health and disease. The eosinophil ribonucleases are secretory mediators from activated eosinophils, such as those noted in our publications as follows: Kraemer LS, Brenner TA, Krumholz JO, Rosenberg HF (2017) A flow-cytometric method to evaluate eosinophil-mediated uptake of probiotic Lactobacillus reuteri. J Microbiol Methods 137:19-24. Foster PS, Maltby S, Rosenberg HF, Tay HL, Hogan SP, Collison AM, Yang M, Kaiko GE, Hansbro PM, Kumar RK, Mattes J (2017) Modeling TH2 responses and airway inflammation to understand fundamental mechanisms regulating the pathogenesis of asthma. Immunol Rev 278:20-40. Percopo CM, Brenner TA, Ma M, Kraemer LS, Hakeem RM, Lee JJ, Rosenberg HF (2017) SiglecF+Gr1hi eosinophils are a distinct subpopulation within the lungs of allergen-challenged mice. J Leukoc Biol 101:321-328. Rosenberg HF (2017) Eosinophils, galectins and a reason to breathe. Proc. Natl. Acad. Sci. USA 113:9139-9141.